[USRP-users] spectral leakage ?!

Amina M. Fellan afellan at hotmail.com
Thu Oct 1 07:53:11 EDT 2015

Hello everybody !
I'm using 2 USRPs N210 equipped with SBX daughterboards with GNU Radio to establish BPSK communication over ISM band. For the latter, I started with the benchmark_tx/_rx.py examples. 
currently I'm trying to measure the SNR at the receiver. I tried using the SNR estimation blocks in the GRC but they seem to be giving erroneous readings, so I decided to try with a spectrum analyzer to estimate the SNR using (S+N)/N. 
I noticed that even when there's no transmission going on, so trying to measure the noise floor, a signal appears on the spectrum and sometimes even not necessarily at the center frequency. This also can be seen using the uhd_fft script from GNU Radio. Attached is a photo of how the spectrum looks if the USRP is on without transmitting/receiving !!
Any clues what is causing this problem ?? 
Thanks for your time !


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